Wireless communication systems, including cellular phones, paging devices, personal communication services (PCS) devices, and wireless data networks, have become ubiquitous in society. The prices of end-user wireless devices, such as cell phones, pagers, PCS systems, and wireless modems, have been driven down to the point where these devices are affordable to nearly everyone and the price of a wireless device is only a small part of the total cost to the end-user. To continue to attract new customers, wireless service providers concentrate on reducing infrastructure costs and operating costs, while improving quality of service in order to make wireless services cheaper and better.
One of the key service quality issues of any wireless network is providing complete and reliable radio frequency (RF) coverage. This is accomplished by eliminating (or at least minimizing) the number of RF “holes” in the geographical area of the wireless network. A hole is an area in which the RF signals from the base station or from the mobile station are blocked by terrain, buildings, vegetation, or any other object. When a wireless device (or mobile station) that is idle, but turned ON, moves into a RF hole, service may be lost (i.e., the mobile station is dropped) because the mobile station cannot receive the pilot channel signal, the paging channel signal, the synchronization channel signal, or other control channel signal. The mobile station must reacquire the wireless network when the mobile station moves out of the RF hole. If the mobile station is ON and active (i.e., handling a voice call or an Internet protocol (IP) data call), the mobile station may drop the call because the forward or reverse traffic channel signal is blocked.
Wireless services providers routinely monitor their wireless networks in order to detect RF holes. Wireless service providers have primarily relied on drive-testing, which uses specialized vehicles to determine coverage holes in the wireless network. Drive-testing is first performed during network launch and is then periodically repeated, depending on the operational plan of the service provider. The periodic tests are necessary to ensure no coverage holes have developed due to change in the terrain (new buildings) and changes in RF parameters in the system. Obviously, the more comprehensive and frequent such tests are, the quicker and more accurate will be the corrective actions of the service provider. However, such specialized tests are expensive to service providers.
During the past few years, pushed by the mobile E-911 effort, advanced location services have been defined to accurately determine the location of mobiles in times of emergency. The solutions for these location services can be mainly categorized into handset-based or network-based. Service providers can try to make use of these location services to determine coverage holes instead of drive tests. Network-based location determination requires that the mobile station location determination circuitry be positioned on network elements (e.g., base stations) in order to correlate power and round-trip delay information from various base stations. Unless the wireless service provider continuously monitors the location of all mobile stations, it is difficult to use that information to determine coverage holes. Also, continually monitoring the positions of all mobile stations consumes an excessive amount of RF bandwidth and processing power in the base stations. Furthermore, network-based location devices determine mobile station location using principles of extrapolation that often prove inaccurate.
Therefore, there is a need in the art for improved systems and methods for determining RF coverage holes in a wireless network. In particular, there is a need for an improved apparatus for determining the location of RF coverage holes in a wireless network that does not require the wireless network to continually monitor the positions of all mobile stations and does not required all mobile stations to continually transmit their position information to the wireless network.